Aquatic Ecological and Human Health Risk Assessment of Chemicals in Wet Weather Discharges in the Sydney Region, New South Wales, Australia     

Gary Bickford  John Toll  Judi Hansen  Elaine Baker  Robert Keessen 《Marine pollution bulletin》1999,39(1-12):335-345

Sydney Water has completed a risk assessment to assess the risks to human health and aquatic organisms in creeks, rivers, estuaries and ocean waters affected by wet weather sewage overflows, stormwater and sewage treatment plant discharges. The risk assessment methodology consists of a comparison of measured and predicted concentrations of chemicals with toxicity reference values. Estimates of receiving water chemical concentrations were derived using data from a 10-year period so that the variable rainfall pattern was represented. Computer models were used to simulate and predict wet weather discharges during this ten year period. Risks were validated by bioassays and bioassessments. Risks to aquatic life from wet weather discharges were attributed to 14 chemicals at one or more of the sites and stormwater was the predominate source of the chemicals. There were no risks to people engaged in water based activities. Noncarcinogenic risks from fish ingestion are predicted at three sites. Predicted cancer risks for most individual chemicals were relatively small. Carcinogenic risks were typically associated with organochlorine compounds, polycyclic aromatic hydrocarbons, dichlorobenzene, and arsenic. The predicted cancer risks also appear to be largely the result of stormwater rather than sewage overflow inputs and largely due to historical contamination by organochlorine pesticides. It is expected the concentrations of these chemicals will decrease over time.  相似文献   

Relationships between lightning activity and various thundercloud parameters: satellite and modelling studies     

M. B. Baker  A. M. Blyth  H. J. Christian  J. Latham  K. L. Miller  A. M. Gadian 《Atmospheric Research》1999,51(3-4)

The lightning frequency model developed by Baker et al. [Baker, M.B., Christian, H.J., Latham, J., 1995. A computational study of the relationships linking lightning frequency and other thundercloud parameters, Q. J. R. Meteorol. Soc., 121, 1525–1548] has been refined and extended, in an effort to provide a more realistic framework from which to examine computationally the relationships that might exist between lightning frequency f (which is now being routinely measured from a satellite, using the NASA/MSFC Optical Transient Detector (OTD)) and a variety of cloud physical parameters. Specifically, superior or more comprehensive representations were utilised of: (1) glaciation via the Hallett–Mossop (H–M) process; (2) the updraught structure of the model cloud; (3) the liquid-water-content structure of the model cloud; (4) the role of the reversal temperature T_rev in influencing lightning characteristics; (5) the critical breakdown field for lightning initiation; and (6) the electrical characteristics of the ice crystal anvil of the model cloud. Although our extended studies yielded some new insights into the problem, the basic pattern of relationships between f and the other parameters was very close to that reported by Baker et al. (1995). The more elaborate treatment of T_rev restricted somewhat the range of conditions under which reverse-polarity lightning could be produced if the cloud glaciated via H–M, but confirmed the earlier conclusion that such lightning would not occur if the glaciation was of the Fletcher type. The computations yielded preliminary support for the hypothesis that satellite measurements of f might be used to determine values of the ice-content of cumulonimbus anvils: a parameter of climatological importance. The successful launch and continuing satisfactory functioning of the OTD [Christian, H.J., Goodman, S., 1992. Global observations of lightning from space, Proc. 9th Int. Conf. on Atmospheric Electricity, St. Petersburg, pp. 316–321; Christian, H.J., Blakesee, R.J., Goodman, S.J., 1992. Lightning imaging sensor (LIS) for the earth observing system. NASA Tech. Memorandum, 4350] make it possible—with a high degree of precision—to measure lightning location, occurrence time and frequency f over extensive areas of the Earth's surface. Measured global distributions of lightning and associated lightning stroke radiance demonstrate that: lightning activity is particularly pronounced over the tropics, much greater over land than over the oceans, and exhibits great seasonal variability; lightning radiance tends to be greater over the oceans, less when lightning activity is high, and greater in the Northern Hemisphere winter than summer.  相似文献   

QUANTIFYING AND MITIGATING FLOOD RISK IN RAPIDLY AGGRADING FLUVIAL SYSTEMS     

Brad R. HALL 《国际泥沙研究》1999,(2)

ILOWERGUADALUPERIVER,SANJOSECALIFORNIATheLowerGuadalupeRiverProjectAreadoesnothavetheabilitytoconveytheflowofthe100-yearfloodevent.LocatedbetweentheSanrranciscoBayandDowntownSanJose,theLowerGuadalupeRiverProjectareaissubjecttomanynaturalandman-inducedagentsandnaturalphysicalprocessesthataffectthehydraulicandsedimenttransportcharacteristicsoftheRiver.Themostsignificantagentsandprocessesincludethelocalgeology,regionalseismicity,tidalprocesses,pastsubsidenceintheregion,risings…  相似文献   

Integrating Stalagmite, Vertebrate, and Pollen Sequences to Investigate Holocene Vegetation and Climate Change in the Southern Midwestern United States     

Rhawn F. Denniston  Luis A. Gonzalez  Holmes A. Semken  Jr.  Yemane Asmerom  Richard G. Baker  Heather Recelli-Snyder  Mark K. Reagan  E. Arthur Bettis  III 《Quaternary Research》1999,52(3):381

Speleothem carbon and oxygen isotopic records from Onondaga Cave, south-central Missouri, and Beckham Creek Cave, north-central Arkansas, are compared with the Cupola Pond and Oldfield Swamp pollen series from southeastern Missouri and the Rodgers Shelter and Modoc Shelter vertebrate biostratigraphic sequences from central Missouri and southwestern Illinois. Similar, and roughly contemporaneous, shifts between deciduous forest and steppe indicators throughout the Holocene are revealed in each database. These independent proxies record steppe conditions between approximately 9000 and 1500 cal yr B.P. A shift toward lighter speleothem carbon may reflect a change from warm and dry to cool and dry conditions between 4500 and 3000 yr B.P. The sensitive response of speleothem δ¹³C to changes in vegetation emphasizes their importance as paleoclimate records in an area containing few other millenial-scale climate proxies.  相似文献   

Seasonal variation in the biogeochemical cycling of seston in Grand Traverse Bay, Lake Michigan     

Eileen M. McCusker  Peggy H. Ostrom  Nathaniel E. Ostrom  Jeffery D. Jeremiason  Joel E. Baker 《Organic Geochemistry》1999,30(12):687

This study describes the biogeochemical cycling of seston in Grand Traverse Bay, Lake Michigan. Seston was characterized by carbon and nitrogen elemental and isotopic abundances. Fluorescence, temperature, light transmittance, and concentrations of dissolved inorganic nitrogen were also determined. PCBs were analyzed from surface (10 m) seston and ΣPCB was calculated by summing all of the congeners quantified in each sample. The vertical and seasonal trends in the δ¹³C values of seston exhibited a broad range from −30.7 to −23.9‰. Low δ¹³C values that occur concurrently with a peak in fluorescence below the thermocline reflect uptake of ¹³C depleted respiratory CO₂ and/or the accumulation of ¹³C depleted lipids by phytoplankton. High δ¹³C values late in the season likely result from a reduction in photosynthetic fractionation associated with a decrease in the CO₂ pool. Seasonal δ¹⁵N values of seston were high in the spring and declined through August. The δ¹⁵N values of seston reflect a balance between fractionation during assimilation of NH₄⁺ or NO₃⁻ and degradative processes. The seston ΣPCB and fluorescence were both high in the spring and subsequently declined, suggesting that the concentrations of PCBs in seston were associated with labile material derived from primary productivity. The strong seasonal trends in the organic geochemical characteristics of seston and concentrations of PCBs emphasize the complex nature of particle cycling in aquatic environments.  相似文献   

Investigating Bermuda's pollution history through stable isotope analyses of modern and museum-held gorgonian corals     

David M. Baker  Thaddeus J.T. Murdoch  Inga Conti-Jerpe  Marilyn Fogel 《Marine pollution bulletin》2017,114(1):169-175

For centuries, Bermuda has been challenged with wastewater management for the protection of human and environmental health. By quantifying the δ¹⁵N of the common sea fan Gorgonia ventalina sampled from 30 sites throughout Bermuda we show that sewage-derived nitrogen is detectable on nearshore coral reefs and declines across the lagoon to the outer rim. We also sampled gorgonians from two museum collections representing a 50y time-series (1958–2008). These samples revealed an increase in δ¹⁵N of > 4.0‰ until the mid-1970s, after which δ¹⁵N values slowly declined by ~ 2.0‰. A δ¹⁵N chronology from a gorgonian skeleton exhibited a similar decline over the last 30–40 years of approximately 0.6‰. We conclude that policies have been effective in reducing sewage impacts to Bermudian reefs. However, significant sources of sewage pollution persist and are likely have a strong impact on harbor and nearshore coral communities and human health.  相似文献   

Mixed sand–mud bedforms produced by transient turbulent flows in the fringe of submarine fans: Indicators of flow transformation     

Megan L. Baker  Jaco H. Baas 《Sedimentology》2020,67(5):2645-2671

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Ecohydrologic feedbacks controlling sizes of cypress wetlands in a patterned karst landscape     

Xiaoli Dong  A. Brad Murray  James B. Heffernan 《地球表面变化过程与地形》2019,44(5):1178-1191

Many landforms on Earth are profoundly influenced by biota. In particular, biota play a significant role in creating karst biogeomorphology, through biogenic CO₂ accelerating calcite weathering. In this study, we explore the ecohydrologic feedback mechanisms that have created isolated depressional wetlands on exposed limestone bedrock in South Florida – Big Cypress National Preserve –as a case study for karst biogeomorphic processes giving rise to regularly patterned landscapes. Specifically, we are interested in: (1) whether cypress depressions on the landscape have reached (or will reach) equilibrium size; (2) if so, what feedback mechanisms stabilize the size of depressions; and (3) what distal interactions among depressions give rise to the even distribution of depressions in the landscape. We hypothesize three feedback mechanisms controlling the evolution of depressions and build a numerical model to evaluate the relative importance of each mechanism. We show that a soil cover feedback (i.e. a smaller fraction of CO₂ reaches the bedrock surface for weathering as soil cover thickens) is the major feedback stabilizing depressions, followed by a biomass feedback (i.e. inhibited biomass growth with deepening standing water and extended inundation period as depressions expand in volume). Strong local positive feedback between the volume of depressions and rate of volume expansion and distal negative feedback between depressions competing for water likely lead to the regular patterning at the landscape scale. The individual depressions, however, are not yet in steady state but would be in ~0.2–0.4 million years. This represents the first study to demonstrate the decoupling of landscape-scale self-organization and the self-organization of its constituent agents. © 2018 John Wiley & Sons, Ltd.  相似文献   

Effectiveness of Monitored Natural Attenuation (MNA) as a Groundwater Remedy for Arsenic in Phosphatic Wastes     

Brad A. Bessinger  Remy J.-C. Hennet 《Ground Water Monitoring & Remediation》2019,39(4):52-68

A study was conducted to evaluate monitored natural attenuation (MNA) as a remedy for arsenic in groundwater at a former phosphate mining and manufacturing facility. The mineralogy, speciation, and lability of arsenic in phosphatic wastes present in soils were characterized using sequential extraction procedures, leaching experiments, batch adsorption tests, and microchemical speciation analysis. A PHREEQC-based reactive transport model was also parameterized using these laboratory results, and it was used to evaluate the importance of identified attenuation mechanisms on arsenic concentrations along a vertical flow path from a shallow, alluvial aquifer to the underlying Floridan aquifer. Arsenic was found to occur in several chemical forms in phosphatic wastes, including unstable sulfide minerals, adsorbed surface complexes, and relatively insoluble phosphate and oxide minerals. Most arsenic was associated with stable minerals. The reactive transport model predicted that historical leaching of solid-phase waste materials in soils would not have generated enough arsenic to explain the concentrations observed in downgradient groundwater; instead, the source of arsenic to groundwater was likely acidic and saline process water that infiltrated though unlined ponds and ditches during historical manufacturing operations. A key factor affecting the long-term effectiveness of natural attenuation of arsenic in groundwater is the occurrence and stability of iron oxyhydroxides in aquifer sediments. According to laboratory and reactive transport model results, sufficient levels were found to be present at the site to effectively limit arsenic migration at concentrations exceeding drinking water standards in the future in the Floridan aquifer. This study presents the geochemical evaluations that are needed to satisfy EPA guidelines on determining whether or not MNA is an acceptable remedy for a site. It specifically details the characterization and modeling that were used to demonstrate effectiveness at a site where MNA was ultimately selected as the remedy for arsenic in groundwater.  相似文献   

不同类型草地挥发性有机物排放特征的研究   总被引：2，自引：1，他引：1  

白建辉  Brad Baker 《大气科学》2006,30(1):119-130

2003年9月,对内蒙古草原不同类型草地挥发性有机物(VOC)的排放、太阳辐射、气象参数等进行观测,结果表明,固定和新的羊草样地、封育样地、不同程度放牧样地异戊二烯、α蒎烯、β蒎烯、柠檬烯、蒈烯的排放均有明显的日变化规律,并与可见光辐射以及温度有较好的一致性.羊草样地、封育样地、过度放牧、适度放牧样地异戊二烯排放的最大值分别为139.5、25.9、132.3、107.1(单位:μg·m-2·h-1,以碳计).多数情况下,异戊二烯排放通量的测定结果为羊草样地高于封育样地、过度放牧样地高于适度放牧样地.不同程度放牧样地α蒎烯、β蒎烯、柠檬烯、蒈烯等的排放具有明显差别,一般是过度放牧草地高于适度放牧草地.剪草增大了绝大部分VOC组分的排放、以及过度和适度放牧草地VOC的排放,剪草可以造成过度和适度放牧草地异戊二烯排放在中午前后的增加.剪草后,过度放牧草地异戊二烯、α蒎烯、β蒎烯、柠檬烯、蒈烯等的排放通量均远大于适度放牧草地的相应值.土壤异戊二烯、α蒎烯、β蒎烯等的排放很小,分别占相近可见光辐射和温度条件下固定羊草样地排放的0.2%、0、3.0%.  相似文献